1. Field of the Invention
This invention relates to an apparatus and method for directly measuring the bottom pour flow rate from crucibles and tundishes of various designs. Examples include inductively heated ceramic crucibles, tundishes used for bottom pouring variety of metals including those used in the plasma arc melting (PAM) process, standard hearth/tundish and the cold hearth process. Such structures of this type generally allow the bottom pour flow rate to be accurately measured in relatively real time without adversely affecting the flow while withstanding the hostile surroundings typically associated with the heated crucibles, PAM, cold hearth process or other similar processes.
2. Description of the Related Art
It is known that in the process of pouring ingots or making powder from a variety of metals and alloys melted in inductively heated ceramic crucibles, or hearth/tundish combinations commonly used in the metals industry, there is a need to know the instantaneous flow rate without any lags. For example, in the powder making process, the flow is measured as the rate of powder collected in a vessel located some distance from the atomizer. This introduces a time delay in the interpretation of the melt flow rate on the order of 1ifs of seconds up to a minute. In order to optimize the yield it is, therefore, critical to directly measure the flow rate (or equivalently velocity) of the melt as it leaves the tundish. Most of the standard techniques, such as venturi meters and vibrating tube mass flow meters, are unacceptable because of the difficulty of constructing such a device to survive in the hostile surroundings and the very limited space available in and around the crucible or tundish for the sensor. The three critical aspects of the problem are the hostile environment, limited space considerations and difficulty of bringing anything but electrical signals from the location of measurement. A more advantageous system, then, would be presented if these three critical aspects could be addressed in a flow rate measuring device.
In order to at least address the aspect of bringing only electrical signals from the location of measurements, a magnetic flow sensing device for measuring the blood flow typically through intravenous (IV) lines has been developed by Fischer and Porter. While these blood flow sensing systems employ an advantageous magnetic measuring device, these systems would not be easily adaptable to a melt from inductively heated ceramic crucibles, a hearth/tundish technique, a PAM process or a cold hearth process due to the space requirements and the hostile environment associated with the prior art processes. In particular, the blood flow sensing device is allowed to occupy a relatively large space around the IV line while the space around the melt guide tube (MGT) of the prior melt flow processes through which the liquid alloy flows is very limited. Also, the temperatures associated with measuring blood typically center around 97.degree.-105.degree. F. (.apprxeq.36.degree.-41.degree. C.) which is far below the temperature associated with the prior alloy melt flow processes which can reach temperatures as high as 3100.degree. F. (.apprxeq.1700.degree. C.). Consequently, a still further improved system would be presented if the advantageous magnetic sensing device could be employed in a relatively small space and could withstand a hostile environment.
It is apparent from the above that there exists a need in the art for an apparatus for measuring the bottom pour flow from a crucible or a tundish which can non-intrusively and directly measure the melt flow rate, and which at least equals the measuring capabilities of known magnetic flow sensing devices, but which at the same time is capable of being located in relatively small spaces and can withstand hostile environments especially those associated with the heated crucible, hearth/tundish combinations, PAM, cold hearth process and other related melt pouring processes. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.